The invention generally relates to electrical switches and more particularly relates to a steering column switch with an electrical connecting device between the steering wheel and the steering column.
DE 44 36 172 A1 discloses an electrical connecting device, in particular, for an airbag restraint accommodated in the hub of the steering wheel. This device contains a stationary housing part and a housing part that can be turned relative to the stationary housing part over a limited angular range, where the housing parts respectively carry a terminal unit and surround a spirally wound, flexible conductor, the ends of which are connected to the terminal units. The connecting device assigned to the hub of the steering wheel comprises a device for displaying the angular position of the housing parts relative to one another. The electrical coupling to the on-board network of the vehicle is realized by way of suitable wire harnesses, so that the installation is associated with relatively high cost, since the connecting device, as well as the required steering column switches, must be electrically connected to the on-board network. In addition, the hub of the steering wheel must be relatively large in order to accommodate the connecting device. The different wire harnesses of the connecting device and the steering column switches also require a relatively large amount of space within the steering column jacket.
Different devices for determining the amount of relative rotation between two elements are known. Here, one element usually consists of a stationary stator in the form of a housing or a holding arrangement, into which a second element that may be mounted on the steering column of the vehicle and that serves as the rotor is rotatably inserted.
In order precisely to determine the angle of rotation, it is common practice to utilize shaft encoders with analog or digital steering angle sensors. Digital steering angle sensors consist, in principle, of an encoded device and a sensor that scans the code, where the encoded device and sensor turn relative to each other. In incremental sensors, the encoded device consists of a disk or wheel with the same type of markings uniformly distributed over the circumference, the said markings are detected by the sensor and signaled by the delivery of corresponding pulses. Successive pulses are counted as a function of the direction of rotation in order to determine the resulting angle of rotation from the accumulated sum. However, it is necessary to define a reference position in order to determine the actual position. This reference position is usually defined in the form of a separate reference or zero marking that can be detected by the sensor. In absolute sensors, the coding is location-dependent, such that an individual signal that directly and unequivocally indicates the given position can be generated for each angular position. However, identical angular positions within successive complete revolutions cannot be geometrically differentiated. This is the reason additional measures must be taken, given the circumstances.
DE 196 49 906 A1 discloses an angular rotation sensor that consists of a sensor housing composed of a housing base part, an upper housing part and a lower housing part. A rotatable sensor shaft with a rotor disk that is arranged on the sensor shaft without rotational play and that carries sliding contacts and with a stator disk that is fixed on the sensor housing without rotational play and that contains several sliding contacts is arranged in the sensor housing. In addition, an electric line extends into the sensor housing, where said line is used to connect the angular rotation sensor to the on-board network of the vehicle. The sensor shaft is realized in the form of a hollow shaft and is provided with interior teeth in one of its two end regions such that it can be coupled to the steering system.
DE 197 55 094 A1 also describes a steering column switch with a unit consisting of an electrical connecting device and a steering angle sensor. The connecting device is arranged in a housing section that forms a cover for the stator of the steering angle sensor mounted on a printed-circuit board, where the printed-circuit board is realized in the form of a base that seals the cover. The interior of the steering column switch is located underneath the printed-circuit board.
DE 44 27 883 C1 discloses an electrically and/or optically functioning device with a holding device. The holding device is fixed on a steering column jacket and forms an integral component with the housing that belongs to an individual switch. A steering column lining is arranged on the holding device. The holding device carries a connecting device that is realized in the form of a spiral cable cassette and a steering angle sensor that is connected to a printed-circuit board. The individual functional components of the device described above are joined by means of fastening elements to form a manageable unit. The connecting device is attached on the side of a housing arrangement of the steering angle sensor assigned to the steering wheel, and the stationary housing part of the connecting device is screwed together with the holding device. The rotatable housing part of the connecting device engages in a circumferential groove in the housing arrangement of the steering angle sensor with a region that is realized in the form of a diaphragm and serves as the rotor.
EP 0 913 319 A2 discloses a steering angle sensor unit with an electrical connecting device that contains a spirally wound conductor and a steering angle sensor, where the steering angle sensor is integrated into the connecting device and the steering angle sensor unit is arranged between the steering wheel and the steering column switch to form a unit. The connecting device contains a cable holder for the conductor which is closed on its underside with a lower housing part. An upper rotor and a lower rotor are inserted into a cylindrical clearance of the cable holder. Thus, the steering angle sensor
The invention is based on the objective of developing a steering column switch of the initially described type which is compact and combines a series of functions, wherein the steering column switch can also easily be installed due to the small number of individual components.
According to the invention, this objective is realized in that the conductor is coupled to a central printed-circuit board that is connected to the on-board network and directly contacted by the stator, where the rotor is realized in the form of a toothed wheel, where the stator comprises an intermediate wheel that is rotationally seated in a stator housing and meshes with the toothed wheel, and where a sensor that is realized in the form of a toothed wheel detects the revolutions of the intermediate wheel.
Consequently, no additional components are required for determining a change in the angular position of the steering column. Moreover, the rotor is fixed to the connecting device that is mounted on the steering wheel so that in any case a separate mounting on the steering column is eliminated. The electrical connection to the on-board network is also realized without additional components, e.g., wire harnesses, since the printed-circuit board of the steering column switch, which also fulfills other functions, is used to realize this connection.
According to an advantageous embodiment of the invention, the rotor is mounted on the cover and the stator is mounted on the upper housing part. The cover that is realized in the form of a rotatable component that spans the conductor of the connecting device undergoes the changes that occur in the angle of rotation synchronously with the steering wheel and thus the steering column. Thus, the rotor changes its position to the same extent as the steering column such that exact measurement values relative to the change in the angle of rotation are acquired.
For mounting purposes, the cover preferably contains a flange on the side of the steering wheel, wherein a coaxial projection for holding the terminal unit of the connecting device and for fixing the rotor is integrally formed on said flange. The flange spans the conductor and essentially lies in one plane with the upper side of the housing part. The terminal unit is used to form the relatively simple electrical connection between the steering wheel and the on-board network. The projection that protrudes from the flange of the cover passes through the free space in the center of the spirally wound conductor, as well as through the surface of the upper housing part on which the conductor lies. Due to the arrangement of the projection in the upper housing part, a defined position relative to the steering column
Thus, an additional function can be integrated into the steering column switch, where the steering angle sensor and the steering column switch form a single structural unit that can be quite easily mounted on a steering column jacket of a motor vehicle. Consequently, no additional components are required for determining a change in the angular position of the steering column. Moreover, the rotor is fixed to the connecting device that is mounted on the steering wheel so that in any case a separate mounting on the steering column is eliminated. The electrical connection to the on-board network is also realized without additional components, e.g., wire harnesses, since the printed-circuit board of the steering column switch, which also fulfills other functions, is used to realize this connection. The change in the angle of rotation can be advantageously monitored and detected without contact if the stator is realized in the form of a sensor that detects the revolutions of the toothed wheel. Such a sensor is not subject to mechanical wear and is of small size. Consequently, the sensor occupies only little space once it is fixed on the upper housing part. In addition, relatively exact measurement data also to be additionally evaluated can be acquired with this sensor. The toothed wheel can be manufactured quite easily and provides the option of detecting a change in the angle of rotation in the form of a change in the position of the teeth, for example, by means of reflected light.
According to an additional refinement of the invention, the rotor is realized in the form of a toothed wheel, the hub of which overlaps the projection of the cover. The toothed wheel can be manufactured quite easily and provides the option of detecting a change in the angle of rotation in the form of a change in the position of the teeth, for example, by means of reflected light or a counting mechanism.
For mounting purposes, the cover preferably contains a flange on the side of the steering wheel, where a coaxial projection for holding the terminal unit of the connecting device and for fixing the rotor is integrally formed on said flange. The flange the conductor and essentially lies in a single plane with the upper side of the housing part. The terminal unit is used to form the relatively simple electrical connection between the steering wheel and the on-board network. The projection that protrudes from the flange of the cover passes through the free space in the center of the spirally wound conductor, as well as through the surface of the upper housing part on which the conductor lies. Due to the arrangement of the projection in the upper housing part, a defined position relative to the steering column is specified which the rotor also assumes.
According to an additional refinement of the invention, the hub of the toothed wheel overlaps the projection of the cover. The projection of the cover is preferably provided with several snap-fit arms that are uniformly distributed over the circumference and engage in corresponding grooves in the hub of the toothed wheel, which ensures the rotationally rigid arrangement of the toothed wheel on the projection and a simple installation of these components.
In order to achieve tolerance compensation and to detect even the slightest changes in the angle of rotation, the intermediate wheel has a smaller circumference than the toothed wheel and is supported on a displaceable, spring-loaded axis. The elastic axis ensures tolerance compensation here because the toothed wheel and the respective toothed wheel sensor have a fixed center of rotation that is represented by the steering column and by an axis on the stator side, respectively. The spring-loaded, displaceable axis is provided for the intermediate wheel because the distance between the steering column and the axis of the toothed wheel sensor varies due to tolerances and an interference-free meshing of the teeth of the toothed wheel and the teeth of the toothed wheel sensor still must be ensured. The intermediate wheel consequently is flexibly supported and assumes a position that corresponds to the respective distance between the steering column and the axis of the toothed wheel sensor.
The stator housing is fixed on guide ridges of the upper housing part by means of snap-fit elements in order to allow the installation of the stator housing without tools. The guide ridges that are realized integrally with the upper housing part not only serve for mounting the stator housing but also for its positioning.
The projection of the cover is preferably provided with several snap-fit aims that are uniformly distributed over the circumference and engage in corresponding grooves in the hub of the toothed wheel, which ensures the rotationally rigid arrangement of the toothed wheel on the projection and a simple installation of these components.
The change in the angle of rotation can be advantageously monitored and detected without contact if the stator is realized in the form of a sensor that detects the revolutions of the toothed wheel. Such a sensor is not subject to mechanical wear and is of small size. Consequently, the sensor occupies only little space once it is fixed on the upper ho using part. In addition, relatively exact measurement data to be evaluated can be obtained with this sensor.
According to an alternative refinement of the invention, the rotor comprises a coded perforated disk, as well as a revolution counter, where the stator comprises several photodetectors assigned to the rotor. The perforated disk, the pattern of which is detected by a photodetector, is used to detect a broad range of changes in the angle of rotation, i.e., between slight changes and changes of one full revolution of the steering wheel or 360xc2x0. The revolution counter is provided for detecting full revolutions of the steering wheel, where the perforated disk intercepts the assigned photodetector after each full revolution, and where this photodetector outputs the corresponding signals to be evaluated.
It is preferred to arrange the perforated disk between the upper housing part and the revolution counter. This means that the perforated disk is located in the immediate vicinity of the guide for the projection of the cover which lies on the housing side and correspondingly fixed in position.
In order to provide a transmitter and a receiver for the photodetectors in the form of an integrated component that can be easily mounted, the photodetectors are realized in the form of forked photodetectors.
In order to realize a wireless electric coupling, the sensor of the stator is preferably connected to the on-board network by means of terminal contacts that contact the printed-circuit board.
The sensor preferably detects a reversal in the direction of rotation of the rotor based on a corresponding metrology, as well as the assignment of the reference marks.
According to another advantageous embodiment of the invention, the sensor transmits the acquired measurement data to the on-board computer for evaluation purposes via the printed-circuit board. Thus, the correspondingly processed measurement data can be directly retrieved by suitable devices via data lines.
The printed-circuit board is preferably used for electrically connecting several individual switches to the on-board network. Consequently, the printed-circuit board combines the electrical functions of the steering angle sensor, the connecting device and the individual switches, for example, windshield wiper/washer switch, blinker switch, headlight switch and/or ignition lock or other electronic safety devices for releasing an ignition lock where the printed-circuit board transmits the corresponding functions to the on-board network of the motor vehicle.